Molecular hydrogen in mantle minerals

Current models assume that hydrogen was delivered to Earth already in oxidised form as water or OH groups in minerals; similarly, it is generally believed that hydrogen is stored in the present mantle mostly as OH.Here we show by experiments at 2-7 GPa and 1100-1300 °C that, under reducing conditions, molecular hydrogen (H 2 ) has an appreciable solubility in various upper mantle minerals.This observation suggests that during the accretion of the Earth, nebular H 2 could have been delivered to the growing solid planet by direct dissolution in a magma ocean and subsequent incorporation in silicates.Moreover, the presence of dissolved molecular H 2 in the minerals of the lower mantle could explain why magmas sourced in this region are rich in hydrogen, despite the fact that lower mantle minerals contain almost no OH groups.